From Michailescu's theorem (Catalan's conjecture) we have that the only $a,b,m,n \in \mathcal{Z}^{+}$ with $m,n>1$ such that $a^{m} - b^{n} = 1$ are: $a=3$, $b=2$, $m=2$, $n=3$.

1) Is there an algorithm which, for any $a,b \in \mathcal{Z}^{+}$ finds the minimum of $|a^{m} - b^{n}|$ $\forall m,n \in \mathcal{Z}^{+}$ (with $m,n>1$ )?

2) Do we know for how many different values of $m,n$ this minimum distance can be achieved?

3) If we do not have such an algorithm, do we know if this problem is decidable?